In order to meet the increasing demand for wireless data traffic since the commercialization of 4G communication systems, the development focus is on the 5th Generation (5G) or pre-5G communication system. For this reason, the 5G or pre-5G communication system is called a beyond 4G network communication system or post Long Term Evolution (LTE) system.
Consideration is being given to implementing the 5G communication system in millimeter wave (mmWave) frequency bands (e.g., 60 GHz bands) to accomplish higher data rates. In order to increase the propagation distance by mitigating propagation loss in the 5G communication system, discussions are underway about various techniques such as beamforming, massive Multiple-Input Multiple Output (MIMO), Full Dimensional MIMO (FD-MIMO), array antenna, analog beamforming, and large scale antenna.
Also, in order to enhance network performance of the 5G communication system, developments are underway of various techniques such as evolved small cell, advanced small cell, cloud Radio Access Network (cloud RAN), ultra-dense network, Device to Device (D2D) communication, wireless backhaul, moving network, cooperative communication, Coordinated Multi-Points (CoMP), and interference cancellation.
Furthermore, the ongoing research includes the use of Hybrid Frequency Shift Keying (FSK) and Quadrature Amplitude Modulation (QAM)(FQAM) and Sliding Window Superposition Coding (SWSC) as Advanced Coding Modulation (ACM), Filter Bank Multi Carrier (FBMC), Non-Orthogonal Multiple Access (NOMA), and Sparse Code Multiple Access (SCMA).
In line with the recent explosive expansion of data traffic in wireless communication networks, demand is increasing for gigabit wireless communication technologies. In order to overcome the limit of data rate expansion based on frequency band expansion, the next generation (beyond 4G) mobile communication systems need to adopt a more-frequency-efficient multiple access technology than Cyclic Prefix-Orthogonal Frequency Division Multiplexing (CP-OFDM). For this reason, the FBMC technology operating without CP is attracting attention. The conventional FBMC technology is capable of improving frequency efficiency by obviating the need of guard band and CP with the use of per-subcarrier filters, in contrast with CP-OFDM technology, which essentially requires the guard band and CP. In particular, the conventional FBMC technology is characterized by the use of an Offset QAM (OQAM) rather than a QAM to guarantee orthogonality between time/frequency resources. That is, because the OQAM-FBMC guarantees orthogonality in the real domain but not in the complex domain, a signal propagating through a complex radio channel experiences intrinsic interference, resulting in difficulty in applying legacy channel estimation and MIMO techniques. Meanwhile, Filtered Multi-Tone (FMT) proposed as a QAM-based FBMC has not attracted much attention because its frequency efficiency is lower than that of CP-OFDM. However, new research published recently has demonstrated a novel QAM-FBMC, which is characterized by transmitting/receiving QAM symbols using a filter designed to cancel or minimize inter-QAM symbol interference with two or more base filters. That is, the OFDM and OQAM-FBMC are Single Pulse (=one prototype filter) Multi-Carrier (SP-MC) schemes, while the QAM-FBMC is a Multi-Pulse Multi-Carrier (MP-MC) scheme.